1. Field of the Invention
The present invention generally relates to a one-shot weft insertion in a jet loom and more particularly, to a method and apparatus for preventing occurrence or generation of a weaving bar (also known as weft bar, filling bar or simply as barre) which may occur due to a low-speed or slow reverse revolution or slow forward revolution of a loom performed during the stoppage of the weaving operation.
2. Description of the Prior Art
For restarting operation of a loom which has been stopped manually or suspended automatically due to occurrence of warp breakage, there is observed a tendency that a thin weaving bar (thin place) is formed in a woven fabric or cloth because of insufficient reed beating force although it depends on the starting characteristic of the loom. Further, when loom operation is stopped due to occurrence of failure in insertion of a weft and is to be restarted after removal of the failure suffering weft, the loom, by revolving at a low speed or slowly in the reverse direction (i.e. reversely or backwardly relative to the direction of weaving), causes fabric just woven and located in the vicinity of the cloth fell to become loosened or slackened and to move rearwardly of the loom from the original or normal position to thereby generate a thick weaving bar (thick place).
For coping with such generation of the weaving bars, there have already been proposed measures or mechanisms for increasing the loom starting torque or correcting the position of the cloth fell prior to the start or restart of the loom, as disclosed, for example, in JP-A-60-231849 (Japanese Patent Application Laid-Open No. 231849/1985), JP-A-61-55241, JP-A-62-263352, Japanese Utility Model Publication No. 94988/1988 and others.
As one type of weaving bar, there is known a so-called "wavy set marks". More specifically, when a cloth fell of a woven fabric is beaten by a reed during the slow reverse or forward revolution of the loom occuring while the weaving operation is suspended, the warps on the cloth fell are displaced in the direction thicknesswise (i.e. upwardly or downwardly) of the woven fabric, as a result of which the corresponding woven portion protrudes from the fabric in a pillow-like configuration. This is herein referred to as the "wavy set mark". Such wavy set mark is likely to be formed in the case of a twill fabric. Of course, in other fabric than the twill, a weaving bar may be formed due to an increase in the weft density in the cloth fell as brought about by the beating during the slow motion of the loom. However, because the weaving bar is generated due to the slow revolution of the loom crankshaft occurring during suspension of the weaving operation, it is impossible to prevent occurrence of the wavy set mark with the weaving bar suppressing means known heretofore as mentioned above which are destined to prevent the weaving bar from occurring when the normal loom motion is restarted.